The invention refers to a process for growing crystals by the Czochralski method using a melt within a crucible, a holden for the crystal to be pulled from the melt, and coaxial to the rotating and pulled crystal holder a separation wall in the form of a hollow cylinder dipping from the melt surface into the melt, and to an equipment for performing the process.
Crystals are grown by the Czochralski method whereby the free-hanging crystal is pulled out of a melt contained in a crucible. Thereby the temperature conditions are precisely monitored. The greatest impact of the Czochralski method is in growth of high-purity crystals for semiconductor technology.
The two-chamber technique allows to reduce segregation effects, to approach a constant composition of melt and thus of the crystals, by supplying fresh melt from a reservoir to that region of the melt from which the crystal is pulled. This is achieved by a hollow cylinder coaxial to the crystal and extending from the melt surface to the crucible bottom to which it is fixed. The supply of melt is achieved through perforations in the separation wall. Such a two-chamber system, or an internal crucible serving a similar purpose, may possibly reduce the axial segregation problem, however, without sufficient reduction of the local segregation problem, the striations problem.
Other processes have become known for the reduction of striations, for instance the reduction of convection by a strong magnetic field. However, these measures require large efforts and, among others, have the disavantages of detrimental effects on electrical properties of the crystals, and of "overheating" of the melt. Furthermore, in case of gallium arsenide the distribution of dislocations is more inhomogeneus than in crystals fabricated without magnetic field.